1. Field of the Invention
This invention relates to method and apparatus for recording a video signal and/or reproducing the video signal so recorded. The invention is more particularly directed to the recording and/or reproducing of a video signal in which a digital information signal, such as a digital version of the audio portion accompanying the video signal, is recorded in a portion of blanking intervals of the video signal. The invention is also directed to a record carrier, such as magnetic tape, on which the video signal is so recorded.
2. Brief Description of the Prior Art
Conventional recording of a video signal and an associated audio signal on tape using a video tape recorder (VTR) involves recording the video signal with a rotary head in a sequence of parallel tracks in an oblique angle to the direction of tape transport, and recording the associated audio signal with one or more fixed heads in one or more longitudinal tracks in the direction of tape transport. Upon playback, the rotary head scans the video track to produce a reproduced video signal while the fixed heads pick up the recorded audio signal.
Home-use VTRs have recently been improved for high density recording to permit long play. That is, recording techniques for home-use VTRs have permitted slow tape speed to be used so that several hours of video programming can be recorded on a single video cassette. More particularly in long play recording, many home-use VTRs have a tape transport speed of only one or two centimeters per second.
Unfortunately, when the tape transport speed is low, as it is during long play recording and playback, the audio tracks are also drawn past the fixed heads at low speed, and the recorded and played back audio signal can lack satisfactory frequency and signal-to-noise characteristics.
In order to avoid this drawback, it is possible to record the audio signal in the oblique video tracks, for example by converting the audio signal to a pulse-code modulated (PCM) digital signal and inserting this PCM signal into horizontal blanking intervals of the video signal.
In high-density recording of a video signal, in order to achieve a satisfactory signal-to-noise ratio in the reproduced video signal, pre-emphasis is applied to the video signal upon recording and corresponding de-emphasis is applied thereto upon playback. However, the amount of pre-emphasis needed for the video signal to achieve an optimum signal-to-noise ratio is not necessarily compatible with the associated PCM signal. For example, in order to achieve optimum picture quality, a pre-emphasis of several tens of dB is applied in the vicinity of 2 MHz, as compared with lower frequencies. However, such strong pre-emphasis can impart a severe phase change to the PCM signal which cannot be corrected by a corresponding de-emphasis during playback. Thus, when subjected to this pre-emphasis and de-emphasis, the PCM signal will become so distorted that the audio information cannot be accurately extracted during playback.